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A modified LLCL-filter with the reduced conducted EMI noise
Wu, Weimin ; Sun, Yunjie; Lin, Zhe; He, Yuanbin; Min, Huang; Blaabjerg, Frede; Chung, Shuhung Chung
Published in:
I E E E Transactions on Power Electronics
DOI (link to publication from Publisher):
10.1109/TPEL.2013.2280672
Publication date:
2014
Document Version
Early version, also known as pre-print
Link to publication from Aalborg University
Citation for published version (APA):
Wu, W., Sun, Y., Lin, Z., He, Y., Huang, M., Blaabjerg, F., & Chung, S. C. (2014). A modified LLCL-filter with the
reduced conducted EMI noise. I E E E Transactions on Power Electronics, 29(7), 3393-3402 . DOI:
10.1109/TPEL.2013.2280672
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IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 29, NO. 7, JULY 2014
3393
A Modified LLCL Filter With the Reduced
Conducted EMI Noise
Weimin Wu, Yunjie Sun, Zhe Lin, Yuanbin He, Min Huang, Frede Blaabjerg, Fellow, IEEE,
and Henry Shu-hung Chung, Senior Member, IEEE
Abstract—For a transformerless grid-tied converter using pulse
width modulation, the harmonics of grid-injected current, the leakage current, and the electromagnetic interference (EMI) noise are
three important issues during designing of the output filter. In this
paper, the common mode and the differential mode EMI noises
are investigated for the LCL- and LLCL-filter-based single-phase
full-bridge grid-tied inverters. Based on this, a modified LLCLfilter topology is proposed to provide enough attenuation on the
conducted EMI noise as well as to reduce the dc-side leakage current. The parameter design method of the filter is also developed.
The comparative analysis and discussion on four filter cases (the
conventional LCL filter, the conventional LLCL filter, the modified
LCL filter, and the modified LLCL filter) are carried out and verified through simulations and experiments on a 0.5-kW, 110 V/50 Hz
single-phase full-bridge grid-tied inverter prototype.
Index Terms—DC-side leakage current, differential mode (DM),
EMI, LCL filter, LLCL filter, single-phase grid-tied inverter.
I. INTRODUCTION
HE photovoltaic power generation has increasingly grown
due to the shortage of fossil fuels. In order to connect the
PV generation panels to the single-phase utility grid, the fullbridge inverter using the pulse width modulation (PWM) has
been widely adopted [1]–[3]. With the merits of more efficient,
less bulky, and less cost than the isolated topology, the transformerless type system catches more attentions [4], [5]. Thus,
the harmonics of grid-injected current, the leakage current, and
the EMI noise are three important issues when designing the PVinverter system, especially for the output filter. For example, the
T
Manuscript received May 31, 2013; revised July 29, 2013 and August 27,
2013; accepted August 30, 2013. Date of current version February 18, 2014. This
work was supported in part by the Project from Shanghai Municipal Education
Commission under Award 13ZZ125, the Project of Shanghai Natural Science
Foundation under Award 12ZR1412400, and the Research Grants Council of the
Hong Kong Special Administrative Region, China under Project CityU 112711.
Part of the work in this paper will be presented at EPE’13 ECCE Europe 15th
European Conference on Power Electronics and Applications, Lille, France.
Recommended for publication by Associate Editor F. Costa.
W. Wu, Y. Sun, and Z. Lin are with Department of Electrical Engineering, Shanghai Maritime University, Shanghai 201306, China (e-mail:
[email protected]; [email protected]; [email protected]).
Y. He and H. S.-h. Chung are with Centre for Smart Energy Conversion and
Utilization Research (CSCR), City University of Hong Kong, Kowloon Tong,
Hong Kong (e-mail: [email protected]; [email protected]).
M. Huang and F. Blaabjerg are with Department of Energy Technology, Aalborg University, 9220 Aalborg, Denmark (e-mail: [email protected];
[email protected]).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TPEL.2013.2280672
Fig. 1. Conventional LLCL-Filter-based single-phase grid-tied inverter connected to an LISN network.
harmonic currents injected into the grid are suggested to satisfy
the standards of IEEE 1547.2-2008 and 519-1992 [6], [7] and
the leakage current and the EMI noise should be below special
requirements based on the safety considerations [8]–[14].
In industrial applications, the cost is an important factor to
select the power filter of the grid-tied inverter. In contrast to
the conventional LCL filter, the LLCL filter can save the total
material as well as the cost since the grid-side inductance can
be reduced a lot [15], [16]. However, the EMI noise attenuation
of the LLCL filter seems to decline due to its small grid inductor
and the additional inductor in the loop of a capacitor.
In this paper, the conducted EMI noise of the LCL filter and
the LLCL filter is first investigated. Then, a modified LLCL filter
structure is proposed and analyzed to suppress the EMI noise
as well as to reduce the leakage current in the photovoltaic
application, when the discontinuous unipolar modulation [17]
is adopted. Third, a design procedure of the modified LLCL filter
is introduced. Finally, comparative analysis and discussion on
the EMI issues are carried out between the conventional LCL
filter, the conventional LLCL filter, the modified LCL filter, and
the modified LLCL-filter-based inverter systems.
II. CONDUCTED EMI NOISE OF HIGH-ORDER
POWER-FILTER-BASED GRID-TIED INVERTER
Fig. 1 shows the configuration of the single-phase full-bridge
grid-tied inverter with the conventional LLCL filter, where the
stray capacitor Cp in the photovoltaic applications is considered
and a simplified line impedance stabilization network (LISN)
module is used as an interface between the inverter and the grid
to measure the EMI noise. For analyzing the common mode
(CM) and the differential mode (DM) EMI noises, the ideal
equivalent of the conventional LLCL-filter-based inverter system
are illustrated in Fig. 2.
0885-8993 © 2013 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.
See http://www.ieee.org/publications standards/publications/rights/index.html for more information.
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IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 29, NO. 7, JULY 2014
= 0.5jωLLISN //(0.5RLISN + 1/2jωCLISN ),
ZLISN 2 = 2jωLLISN //(2RLISN + 2/jωCLISN ), and Zf =
jωLf + 1/jωCf .
As shown in Fig. 1, if the resonant inductor Lf is shortened,
then the conventional LCL-filter-based system is obtained. For
analyzing the CM voltage noise, the ideal equivalent circuit of
the conventional LCL-filter-based system is the same as that of
the conventional LLCL filter, which is also shown in Fig. 2(a).
The related attenuation gain on the CM voltage noise can also
be depicted with (2). If the resonant inductor Lf as shown in
Fig. 2(b) is set to zero, the equivalent circuit of the conventional
LCL-filter-based system for analyzing the DM voltage noise can
also be obtained. Then, the attenuation gain on conducted DM
voltage noise through the ideal conventional LCL filter can be
calculated as
≈ −20 log10 (jωL2
AttDM L C L (ω) [dB] where
ZLISN
1
ω ≥2π ·150kHz
Fig. 2. Equivalent circuit of the conventional LLCL-filter-based system for
analyzing (a) common mode (CM) voltage noise (b) differential mode (DM)
voltage noise.
+ ZLISN
1/
jωCf
+ 20 log10 1
jωL2 + /jωCf + ZLISN 2 jωLLISN
.
+ 20 log10 1
RLISN + /jωCLISN + jωLLISN The components of the CM voltage noise VCM (t) and DM
voltage noise VDM (t) can be calculated as
VAN (t) + VBN (t)
, VDM (t) = VAN (t) − VBN (t)
2
(1)
where, VAN (t) and VBN (t) are the terminal voltages of the two
phase legs with respect to the midpoint of the split dc capacitors
N , as labeled in Fig. 1.
Within the frequency range of 150 kHz–1 MHz, the attenuation gains on the CM and DM voltage noises through the ideal
conventional LLCL filter can be approximately derived with (2)
and (3), respectively
≈ −20 log10 0.25jω(L1 +L2 )
AttCM L L C L (ω)[dB]
VCM (t) =
ω≥2π·150 kHz
jωLLISN 1 + 20 log10 2
1
+ ZLISN
+
2jωCP
RLISN
1
jωLLISN − 20 log10 +
+
2
2jωCLISN
2
+ 20 log10
AttDM
(ω)[dB]
LLC L
vDM (t) = αUdc cos (ω0 t) +
× Jn (mπα) sin
vCM (t) =
(2)
ω ≥2π ·150 kHz
≈ −20 log10 (jωL2
+ ZLISN 2 )//Zf + jωL1 + 20 log10 (2RLISN )
Zf
+ 20 log10 jωL2 + Zf + ZLISN 2 jωLLISN
+ 20 log10 1
RLISN + /jωCLISN + jωLLISN (4)
For the single-phase full-bridge inverter application, the
unipolar PWM method is popular as it causes less switching
power losses. When the asymmetrical regular sampled discontinuous unipolar PWM method [17] is adopted, the spectrum of
the DM and CM voltage noise generated by an ideal full-bridge
single-phase inverter can be depicted as
+
RLISN
2
1
2 )// /jωCf + jωL1 + 20 log10 (2RLISN )
αUdc
−
π
∞
∞
2Udc 1 π m =1 m n =−∞
nπ
cos (mωs t + nω0 t)
2
∞
cos n π
2αUdc 2
π
n =2
(n + 1) (n − 1)
(5)
cos (nω0 t)
∞
∞
4Udc 1 1
J2k −1 (mπα) cos (mωs t)
π 2 m =1 m
2k − 1
k =1
−
4Udc
π2
∞
m =1
× (mπα)
∞
∞
1 J2k −1
m n =−∞
k =1
(2k − 1) cos n2π
(n + 2k − 1) (n − 2k + 1) |n |= 2k −1
· cos (mωs t + nω0 t)
(6)
where α is the modulation index, Udc is the dc-link voltage, Jn
are
Bessel functions [17], and ω0 and ωs are the fundamental and
(3)
the switching frequencies in radians per second, respectively.
WU et al.: MODIFIED LLCL FILTER WITH THE REDUCED CONDUCTED EMI NOISE
3395
TABLE I
PARAMETERS OF THE INVERTER FOR SIMULATION AND EXPERIMENT
Fig. 4. Proposed modified LLCL-filter-based single-phase grid-tied inverter
and the measuring system.
PWM method is adopted. It can be seen that for the conventional
LLCL-filter-based system, both the simulated attenuation on the
CM and DM voltage noises cannot meet with the standards of
CISPR Class A or Class B, while for the conventional LCL filter,
CM voltage noise cannot meet with the EMI standards. Therefore, for a conventional high-order power-filter-based system,
in order to ensure the EMI noise to meet the requirement of
standards of CISPR, further measures should be taken.
III. PROPOSED MODIFIED LLCL FILTER
Fig. 3. Simulated ac-side conducted EMI voltage noise (a) conventional LLCL
filter (b) conventional LCL filter.
During the EMI noise analysis, note that the total EMI noise
should not only be related to the background EMI noise caused
by the auxiliary power supply of the controller, but also depend
much on the parasitic parameters, which are closely related to
the circuit layout and the character of the switches [18]–[20].
However, according to [21] and [22], within the frequency range
of 150 kHz∼1 MHz, the EMI effect caused by parasitic parameters of the output filter is not so serious. So in order to further
illustrate the EMI noise for a high-order power-filter-based system within the frequency range of 150 kHz∼1 MHz, the simulations are carried out, where the parameters are listed in Table I
under the condition of that Udc = 175 V, Ug = 110 V/50 Hz,
Prated = 500 W, and the switching frequency is 20 kHz. The
parameters of the filters mainly depend on the harmonic current
requirement of IEEE 1547.2-2008 and 519-1992 and the design
procedure has been introduced in [15].
Under the ideal conditions, within the frequency range of
150 kHz–1 MHz, the simulated maximum amplitude of the conducted CM and DM voltage noises for the conventional LLCL
filter and LCL-filter-based single-phase full-bridge grid-tied inverters are shown in Fig. 3, where the discontinuous unipolar
Recently, Dong et al. [23] proposed an interesting method
to suppress the leakage current of the LCL-filter-based singlephase grid-tied inverter system. In this paper, a similar structure
is proposed for the LLCL-filter-based inverter as shown in Fig. 4.
Compared with the conventional LLCL-filter, two extra split CM
capacitors of CCM are inserted in parallel with the Lf –Cf resonance circuit. The mid-point of the extra split CM capacitors is
linked with the midpoint of the split dc capacitors Cdc S . Then,
most of the high-frequency CM voltage noise passes through the
split capacitor branch. At the same time, the series noninductive
split CM capacitors also do suppress the DM voltage noise.
For the modified LLCL-filter-based system, the ideal equivalent circuits for analyzing the CM and DM voltage noises are
illustrated in Fig. 5. The attenuation gains on suppressing the
CM and DM voltage noise can approximately be calculated as
≈ −20 log10 (0.25jωL2
ω ≥2π ·150kHz
1
1
+ ZLISN 1 + /2jωCp )// /jωCS + 0.25jωL1 1
1
− 20 log10 0.25jωL2 + ZLISN 1 + /2jωCp + /jωCS AttCM L L C L
(ω) [dB] − 20 log10 jωCS 1
− 20 log10 0.5jωLLISN + /2jωCLISN + 0.5RLISN jωLLISN RLISN
+ 20 log10
+ 20 log10 2
2
(7)
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IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 29, NO. 7, JULY 2014
Fig. 5. Equivalent circuit of the modified LLCL-filter for analyzing (a) CM
voltage noise (b) DM voltage noise.
AttDM
(ω)
[dB]
LLC L
+ ZLISN 2 )//Zf
1
ω ≥2π ·150kHz
≈ −20 log10 (jωL2
+ jωL1 + 20 log10 (2RLISN )
Fig. 6. Simulated conducted EMI noise for the system with (a) modified LCL
filter (b) modified LLCL filter.
Zf 1
+ 20 log10 jωL2 + Zf 1 + ZLISN 2 jωLLISN
(8)
+ 20 log10 1
RLISN + /jωCLISN + jωLLISN Cd c s
where Cs = C2CC MC M+C
, Zf 1 = (jωLf + 1 jωCf )//2 jωCCM .
dc s
Similarly, as shown in Fig. 4, if the Lf is shortened, then the
modified LCL-filter-based system, which is the same as the filter
structure proposed by Dong et al. [23], is obtained. The ideal
equivalent circuit of the modified LCL-filter-based system for
analyzing the CM voltage noise is also shown in Fig. 5(a) and
the attenuation gain of the CM voltage noise can be calculated
with (7). The equivalent circuit for analyzing DM voltage noise
can be obtained when Lf is shortened in Fig. 5(b) and the related
attenuation gain can be depicted as
AttDM L C L (ω) [dB] ≈ −20 log10 (jωL2
ω ≥2π ·150kHz
+ ZLISN
1
2 )// /jω(Cf + 0.5CCM ) + jωL1 + 20 log10 (2RLISN )
1/
jω(Cf + 0.5CCM )
+ 20 log10 1
jωL2 + /jω(Cf + 0.5CCM ) + ZLISN
jωLLISN
.
+ 20 log10 1
RLISN + /jωCLISN + jωLLISN 2
(9)
Based on the parameters of Table I, the simulated maximum
amplitudes of the attenuations on the CM and DM voltage noises
for the modified LLCL and LCL filter are shown in Fig. 6.
Compared with Fig. 3, it can be seen that the attenuation on the
EMI noise within the frequency range of 150 kHz∼1 MHz has
been improved a lot.
IV. DESIGN OF THE MODIFIED LLCL FILTER
A. Constraints on Harmonics of the Grid-Injected Current
and EMI Noise Within 150 kHz∼1 MHz
In [15], the design of the conventional LLCL filter has been
introduced step by step based on the requirements of five limits,
which were also discussed in [24] and [25]. For the modified
LLCL filter, the parameters of the inverter-side inductor and the
Lf − Cf resonant circuit are similar to those of the conventional
LLCL filter. This paper will focus on designing the grid-side
inductor and the additional split CM capacitor. Certainly, the
trial and error method is still used for the design. The additional
split CM capacitor depends on the rule of 0.5CCM + Cf ≤
5% P r a t e d
ω o V g V g , where Prated is the rated output power of inverter
and Vg is the RMS value of the grid voltage. In this paper,
the additional split CM capacitor is first selected as 0.5CCM =
Pra te d
Cf = 1.5%
ωo Vg Vg .
The transfer function of the grid-injected current versus the
output voltage for the modified LLCL-filter-based inverter can
WU et al.: MODIFIED LLCL FILTER WITH THE REDUCED CONDUCTED EMI NOISE
3397
Fig. 8. Equivalent circuit for analyzing the leakage current based on modified
LCL or LLCL filter.
Fig. 7. Bode diagrams of the grid-injected current versus the ac output voltage
for the LLCL-filter-based grid-tied inverter.
be derived as
Gu i →i g (s) =
= ig (s) ui (s) s=j ω
ZC (s)
(10)
Z1 (s) Z2 (s) + Z1 (s) ZC (s) + Z2 (s) ZC (s) s=j ω
Z1 (s) = sL1 , Z2 (s) = sL2 , ZC (s) = (1/0.5s CCM )//
(sLf + 1/sCf ).
Fig. 7 shows the Bode diagrams of the grid-injected current
versus the ac output voltage for the LLCL-filter-based grid-tied
inverter system. It can be seen that owing to the Lf − Cf resonant circuit, the current harmonics around the switching frequency have been attenuated to over 80 dB both for the conventional LLCL filter and the modified LLCL-filter-based system.
If harmonics around the double of the switching frequency are
small enough, then the harmonic current requirements of the
IEEE 519-1992 can be met. Therefore, the criteria to choose the
grid-side L2 of the modified LLCL filter is expressed as
where
Ud c
π
|max(|J1 (2πα)|, |J3 (2πα)|, |J5 (2πα)|)|×|Gu i →i g (j2ωs )|
Iref
≤ 0.3%
(11)
where Iref is the rated reference peak current.
B. Constraints on Leakage Current
In many applications, such as in photovoltaic generation, if
it is done without galvanic isolation, the inverter will generate
a variable CM voltage and the leakage current (CM current)
appears in the stray capacitor between the PV array and the
protection earth [26]. So for safety considerations, the leakage
current should be limited to a required level [27].
For the modified LLCL-filter-based system, the equivalent
circuit for analyzing the leakage current is given in Fig. 8. The
split CM capacitors provide a high-frequency attenuation loop
on the CM voltage noise as well as the dc leakage current. The
negative dc-rail voltage with respect to the earth vdc N and the
Fig. 9.
Photo of the modified LLCL-filter-based inverter prototype.
leakage current can be approximately estimated as
vdc
N
≈−
vCM (ω)
2 − 0.5Vdc + 0.5Vg
1 − ω/ωr
ileakage
∞
∞
≈
[2 (mωs + nω0 ) · Cp · vdc
(12)
N
(mωs + nω0 )]2
m =1 n =−∞
(13)
C M +C d c s )
where ωr = 2(C
L 1 ·C C M ·C d c s , Vg is the grid voltage, Vdc is the
dc-link voltage of the inverter, and ileakage is the RMS value of
the leakage current.
When CCM and L2 are selected, the EMI requirement within
the frequency of 150 kHz–1 MHz should be verified with (7) and
(8), where the total EMI noise requirement should be met. If it is
necessary, a coupled CM inductor LCM needs to be connected
with the inverter-side inductor to further reduce the CM EMI
noise and the leakage current.
V. EXPERIMENTAL RESULTS
In order to confirm the effectiveness of the proposed modified
LLCL filter on suppressing the conducted EMI noise, a 500-W
prototype of the single-phase full-bridge grid-tied inverter with
the DSP (TMS320LF2812A) controller is constructed. The experiments are evaluated and investigated under the given conditions of fs = 20 kHz, Udc = 175 V, Ug = 110 V/50 Hz,
Prated = 500 W, and the discontinuous unipolar PWM
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IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 29, NO. 7, JULY 2014
Fig. 10. Measured power spectrum results of the grid-injected current with four type power-filter-based system (a) conventional LCL filter (b) conventional LLCL
filter (c) modified LCL filter (d) modified LLCL filter.
TABLE II
ATTENUATIONS ON THE MAXIMUM HARMONIC CURRENT FOR FOUR
DIFFERENT FILTER BASED SYSTEMS AROUND THE SWITCHING FREQUENCY
AND THE DOUBLE OF THE SWITCHING FREQUENCY
modulation method is adopted. The experimental parameters of
the filter are the same as those for simulations listed in Table I.
The photo of the modified LLCL-filter-based inverter system
is shown in Fig. 9. Note that the size of the L2 is much smaller
than L1 . Certainly, the further optimization on the design of
total filter need be carried out to minimize the total size and the
footprint.
The experimental results on the power spectrum of the gridinjected current, the conducted EMI noise in the grid-side, the
negative dc-rail voltage with respect to the earth vdc N and the
leakage current of four filter cases are given in Figs. 10–14,
respectively.
A. Power Spectrum of the Grid-Injected Current
Fig. 10 shows measured power spectrum of the grid-injected
current for four different types of the power-filter-based system.
Table II shows the measured attenuations on the maximum
harmonic current for four different filter-based systems around
the switching frequency and the double of the switching fre-
quency. It can be seen that compared with the conventional LCL
filter and the modified LCL filter, the conventional LLCL filter and the modified LLCL filter have better attenuating effects
on the harmonics of the grid-side current around the switching
frequency, but the opposite around the double of the switching
frequency. The modified LLCL filter has a better attenuation on
the harmonic than the conventional LLCL filter around the double of the switching frequency due to the extra series split CM
capacitors.
B. Measured Conducted EMI Noise
A spectrum analyzer (Agilent E4402) and LISN (EMCO
4825) are used to measure the EMI noise. In the spectrum analyzer, the peak value of the conducted EMI voltage is tracked.
Fig. 11 shows the measured background EMI noise when the
auxiliary power supply of the controller is ON and output PWM
signals are all blocked for four different types of system. It can
be seen that the background EMI noise is close to the standards
of CSIPR 11 class B around the frequency of 150 kHz. It should
be pointed out that no extra ac EMI filter is inserted during the
test.
Fig. 12 shows the measured grid-side conducted EMI voltages
of four type power-filter-based systems. It can be seen that for
the conventional LLCL filter or LCL-filter-based system, the
total conducted EMI noise cannot meet the standards of CSIPR
11 class A. But for the modified LLCL filter or LCL-filter-based
system, the total conducted EMI noise can meet the standards
of CSIPR 11 class A. Comparing the parameters of the modified
WU et al.: MODIFIED LLCL FILTER WITH THE REDUCED CONDUCTED EMI NOISE
Fig. 11. Measured background conducted EMI noise for different filter-based
system (a) conventional LCL filter, (b) conventional LLCL filter, (c) modified
LCL filter, (d) modified LLCL filter.
3399
Fig. 12. Experimental results of conducted EMI noise for different filter-based
system (a) conventional LCL filter (b) conventional LLCL filter (c) modified LCL
filter (d) modified LLCL filter.
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IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 29, NO. 7, JULY 2014
Fig. 13. Measured waveforms of the negative dc-rail voltage with respect
to the protection earth (v d c N ) and the leakage current for the conventional
LLCL-filter-based system (a) v d c N (b) leakage current.
LLCL filter with the modified LCL filter as listed in Table I, it
can be seen that the total inductance of the LLCL filter is smaller
about 20% than that of the LCL filter.
C. Negative DC-Rail Voltage With Respect to the Earth vdc
and the Leakage Current
N
In the photovoltaic inverter application, the stray capacitance
between the PV array and the protection earth is generally proportional to the power rating of the inverter system. In the experimental prototype, two capacitors of 44 nF are used to emulate
the stray capacitors of CP as shown in Figs. 1 and 4. For the
conventional LLCL filter and the modified LLCL-filter-based
systems, the measured waveforms of the negative dc-rail voltage with respect to the protection earth vdc N and the leakage
current are shown in Figs. 13 and 14, respectively. It can be seen
that with the modified LLCL-filter structure, the negative dc-rail
voltage of the system is much smooth and the RMS value of the
leakage current can be attenuated from 664 to 10.3 mA, which
can meet the standards given in DIN V VDE V 0126-1-1 [27].
Note that the leakage current waveform of the modified LCLfilter-based system is similar to the modified LLCL filter and the
measured RMS value of the leakage current is 9.4 mA, which
can also meet the standards given in DIN V VDE V 0126-1-1
well.
Fig. 14. Measured waveforms of the negative dc-rail voltage with respect to
the protection earth (v d c N ) and the leakage current for the modified LLCLfilter-based system (a) v d c N , (b) leakage current.
VI. CONCLUSION
This paper analyzes and addresses the conducted EMI issues
for the high-order power-filter-based single-phase full-bridge
grid-tied inverter using the discontinuous unipolar modulation.
The following can be concluded.
1) If the extra ac EMI filter is not inserted, both the CM
and the DM EMI noises cannot meet the requirements of
CISPR 11 for the conventional LLCL-filter-based system,
while the CM EMI noises cannot meet the requirements of
CISPR 11 for the conventional LCL-filter-based system.
2) Compared with the conventional LCL and LLCL filter,
the attenuation on EMI noise of the modified LCL- and
LLCL-filter-based inverter systems has been improved a
lot.
3) Compared with the conventional LLCL filter, the RMS
value of the leakage current of the modified LLCL-filterbased system decreases from 664 to 10.3 mA for a 500-W
prototype with two stray capacitors of 44 nF, which fully
meets the leakage current requirement of DIN V VDE V
0126-1-1 [27].
4) Compared with the LCL filter, the modified LLCL filter can
save about 20% of the total inductance. Note that currently,
our work focuses on the principle of this new topology,
more work needs to be carried out on the integration of
the filter to minimize the size and the footprint.
WU et al.: MODIFIED LLCL FILTER WITH THE REDUCED CONDUCTED EMI NOISE
A design method of the proposed modified LLCL filter has
also been introduced. The theoretical analysis has been fully
verified through simulations and experiments on a 500-W,
110 V/50 Hz prototype with four different type of power-filter
structure. The experimental results are greatly in agreement with
the theoretical analysis.
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Weimin Wu received the B.S. degree from the Department of Electrical Engineering, Anhui University of Science and Technology, Huainan, China, in
1997, the M.S. degree from the Department of Electrical Engineering, Shanghai University, Shanghai,
China, in 2001, and the Ph.D. degree from the College of Electrical Engineering, Zhejiang University,
Hangzhou, China, in 2005.
He was a Research Engineer in Delta Power Electronic Center (DPEC), Shanghai, from July 2005 to
June 2006. Since July 2006, he has been a Faculty
Member at Shanghai Maritime University, Shanghai, where he is currently an
Associate Professor in the Department of Electrical Engineering. He was a Visiting Professor in the Center for Power Electronics Systems (CPES), Virginia
Polytechnic Institute and State University, Blacksburg, VA, USA, from September 2008 to March 2009. From November 2011 to January 2014, he is also
a Visiting Professor in the Department of Energy Technology, the Center of
Reliable Power Electronics (CORPE), Aalborg University, Aalborg, Denmark.
He has coauthored about 40 papers in technical journals and conferences. He
is the holder of three patents. His research interests include power converters
for renewable energy systems, power quality, smart grid, and energy storage
technology.
Yunjie Sun was born in Heilongjiang Province,
China, in 1988. He received the B.S. and M.S. degrees from the Department of Electrical Engineering,
Shanghai Maritime University, Shanghai, China, in
2011 and 2013, respectively.
He is currently with Action-Power Company Ltd.,
Xi’an, China. His current research interests include
digital control technique, power quality compensator,
and renewable energy generation system.
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IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 29, NO. 7, JULY 2014
Zhe Lin received the B.S. degree from Anhui University, Hefei, China, in 2011 and the M.S. degree from
Shanghai Maritime University, Shanghai, China, in
2013.
He is currently a Research Assistant at the Centre for Smart Energy Conversion and Utilization Research, City University of Hong Kong, Kowloon,
Hong Kong. His current research interests include
control of power converters and renewable energy
application.
Yuanbin He received the B.Eng. and M.Eng. degrees
in electrical engineering, Shanghai Maritime University, Shanghai, China, in 2009 and 2011, respectively.
He is currently working toward the Ph.D. degree in
power electronics at City University of Hong Kong,
Kowloon, Hong Kong.
He was an Associate Researcher in Nanjing FSPPowerland Technology Technology Inc., Nanjing,
China, until March 2013, where he has been involved
in research and development of dc–dc and dc–ac converters. His current research interests include digital
control technique and renewable energy generation system.
Min Huang was born in Hunan Province, China, in
1988. She received the B.S. degree from the Department of Electrical Engineering, Shanghai Maritime
University, Shanghai, China. She is currently working toward the Ph.D. degree in the Institute of Energy
Technology, Aalborg University, Aalborg, Denmark.
Her research interests include power quality,
control and power converters for renewable energy
systems.
Frede Blaabjerg (S’86–M’88–SM’97–F’03) received the Ph.D. degree in 1995 from Aalborg University, Aalborg, Denmark.
He was with ABB-Scandia, Randers, Denmark,
from 1987 to 1988. He became an Assistant Professor
in 1992, an Associate Professor in 1996, and a Full
Professor of power electronics and drives in 1998,
with Aalborg University, Aalborg, Denmark. He has
been a part time Research Leader with the Research
Center Risoe in wind turbines. From 2006 to 2010,
he was the Dean of the Faculty of Engineering, Science, and Medicine and became a Visiting Professor with Zhejiang University,
Hangzhou, China, in 2009. His current research interests include power electronics and its applications such as in wind turbines, PV systems, reliability,
harmonics and adjustable speed drives.
He received the 1995 Angelos Award for his contribution in modulation
technique and the Annual Teacher Prize at Aalborg University. In 1998, he received the Outstanding Young Power Electronics Engineer Award by the IEEE
Power Electronics Society. He has received 14 IEEE Prize Paper Awards and
another Prize Paper Award at PELINCEC Poland in 2005. He received the IEEE
PELS Distinguished Service Award in 2009, the EPE-PEMC Council Award in
2010, and the IEEE William E. Newell Power Electronics Award 2014. He has
received a number of major research awards in Denmark. He was an Editorin-Chief of the IEEE TRANSACTIONS ON POWER ELECTRONICS from 2006 to
2012. He was a Distinguished Lecturer for the IEEE Power Electronics Society
from 2005 to 2007 and for the IEEE Industry Applications Society from 2010
to 2011. He was a Chairman of EPE in 2007 and PEDG, Aalborg, in 2012.
Henry Shu-hung Chung (M’95–SM’03) received
the B.Eng. degree in 1991 and the Ph.D. degree in
1994 in electrical engineering, both from The Hong
Kong Polytechnic University, Hung Hom, Hong
Kong.
Since 1995, he has been with the City University
of Hong Kong (CityU), Kowloon, Hong Kong, where
he is currently a Professor of the Department of Electronic Engineering and the Director of the Centre for
Smart Energy Conversion and Utilization Research.
His research interests include time- and frequencydomain analysis of power electronic circuits, switched-capacitor-based converters, random-switching techniques, control methods, digital audio amplifiers,
soft-switching converters, and electronic ballast design. He has authored six
research book chapters, and more than 300 technical papers including 140 refereed journal papers in his research areas, and holds 26 patents.
Dr. Chung is currently the Chairman of Technical Committee on HighPerformance and Emerging Technologies of the IEEE Power Electronics Society, and an Associate Editor of the IEEE TRANSACTIONS ON POWER ELECTRONICS, the IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS, PART I: FUNDAMENTAL THEORY AND APPLICATIONS, and the IEEE JOURNAL OF EMERGING AND
SELECTED TOPICS IN POWER ELECTRONICS.